Plant growth regulators are useful for influencing a range of plant developmental processes including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, fruit size and quality, as well as leaf and fruit senescence. Plant growth regulators may be formulated in at least five different types of formulations: 1) solutions, 2) wettable powders, 3) soluble powders, 4) tablets and 5) water-dispersible granules. In order to use such formulations, they must be diluted in aqueous solution prior to conventional spray application. Each of the conventional types of formulations has disadvantages, so research to provide improved plant growth regulator formulations continues. The disadvantages of the conventional formulations will be discussed with reference to a specific plant growth regulator class, the gibberellins, as representative of conventional formulations of plant growth regulators in general.
Gibberellins are one class of plant growth regulators which are diterpenoid acids. Gibberellins are commercially produced by fermentation of a natural fungus, Gibberella fugikuroi. Gibberellins are marketed under various trade names and are commercially used on a variety of fruit orchards, vegetable crops, row crops, and ornamental crops. The predominantly used gibberellic acid is GA3, formulated in any of the five forms described above. The other commonly used gibberellins are a combination of two, (GA4+7) which are primarily formulated as solutions either in tetrahydrofurfurryl alcohol (THFA) or in propylene glycol.